Spark-advance control apparatus for internal combustion engine

Abstract

An apparatus for controlling spark advance in an internal combustion engine of an automotive vehicle, characterized by a circuit arrangement which is operative to detect the angular speed of rotation of the engine output shaft in a digital fashion and produce digital signals responsive to changes in preselected operating conditions such as engine output speed and intake manifold vacuum for controlling the spark advance in accordance with predetermined schedules. The spark advance is thus controlled without being affected by negligible or incidental transient fluctuations in the operating conditions of the engine and the advance characteristics can be readily altered by varying the schedules on which the digital signals are produced.

What is claimed is: 
     
       1. An apparatus for controlling spark advance in an internal combustion engine having an output shaft and an intake manifold, the apparatus comprising, in combination: analog signal generating means responsive to output speed of the engine and to vacuum in said engine intake manifold for producing an analog signal which varies with detected engine output speed with the detected intake manifold vacuum in accordance with respective predetermined schedules,   digital signal generating means responsive to preselected operating parameters which affect performance characteristics of the engine for producing a first train of impulses with a frequency related to said parameters,   detecting means responsive to rotational motion of the output shaft of the engine for producing a second train of impulses each representative of a timing at which a respective piston in each cylinder of said engine reaches a predetermined position relative to its associated engine cylinder and a third train of impulses having a frequency proportional to angular displacement of said output shaft,   a computing circuit coupled to said detecting means to said digital signal generating means and to said analog signal generating means and responsive to each of the impulses of said second train of impulses from said detecting means for passing therethrough impulses of said first train of impulses from said digital signal generating means for a period of time which varies with the analog signal from said analog signal generating means in accordance with a predetermined schedule,   a memory circuit for temporarily registering the impulses passed through said computing circuit from said digital signal generating means during each time interval between the impulses of said second train of impulses from said detecting means, and   a preset counter circuit connected to said detecting means and to said memory circuit and responsive to signals therefrom for producing a spark-advance control signal at a timing which is advanced in proportion to that number of impulses registered in said memory circuit from said digital signal generating means in a time period immediately preceding each of said time intervals between the impulses of the second train of impulses from said detecting means and to the frequency of the impulses of the third train of impulses from said detecting circuit impressed on the counter circuit during each of said time intervals.   
     
     
       2. An apparatus as set forth in claim 1, in which said counter circuit produces a basic potential proportional to the number of the impulses registered in said memory circuit in the time period immediately preceding each of said time intervals and an additional potential stepwise increasing with the impulses of said third train of impulses successively impressed on the counter circuit from said detecting means during each of said time intervals and to compare the sum of the basic and additional potentials with a predetermined reference potential for producing said spark-advance control signal when said sum becomes equal to said reference potential. 
     
     
       3. An apparatus as set forth in claim 1, in which said counter circuit produces a basic potential proportional to the reciprocal of the number of the impulses registered in said memory circuit in the time period immediately preceding each of said time intervals and an additional potential stepwise increasing with the impulses of said third train of impulses successively impressed on said counter circuit from said detecting means during each of said time intervals and to subtract said additional potential from said basic potential for producing said spark-advance control signal when the difference between the basic potential and the additional potential becomes zero. 
     
     
       4. An apparatus as set forth in claim 1, in which said analog signal generating means comprises an engine speed sensor for detecting output speed of the engine and producing an output voltage related to the detected engine output speed, an intake-manifold vacuum sensor for detecting vacuum in the engine intake manifold and producing an output voltage related to the detected intake-manifold vacuum, a first function generator responsive to the output voltage from said engine speed sensor for producing a first signal voltage varying with said output voltage of the engine speed sensor in accordance with a predetermined schedule, a second function generator responsive to the output voltage from said intake-manifold vacuum sensor for producing a second signal voltage varying with the output voltage of the vacuum sensor in accordance with a predetermined schedule, and a voltage adding circuit for producing a signal voltage equal to the sum of the first and second signal voltages from said first and second function generators. 
     
     
       5. An apparatus as set forth in claim 1, in which said computing circuit comprises a saw-tooth wave generator responsive to each of said impulses of said second train of impulses from said detecting means for producing a ramp pulse having a duration shorter than each of said time intervals between said impulses of said second train of impulses from the detecting means and a risetime. concurrent with each of said impulses of said second train of impulses from the detecting means, a comparator for comparing said analog signal from said analog signal generating means with said ramp pulse for producing a square-shaped pulse when the former is higher than the latter, and circuit means for passing therethrough the impulses from said digital signal generating means to said counter circuit in the presence of the square-shaped pulse from said comparator. 
     
     
       6. An apparatus as set forth in claim 1, in which said digital signal generating means comprises a signal generator responsive to said preselected parameters for producing an output voltage which varies with the parameters in accordance with a predetermined schedule and an impulse generator operative to produce a train of impulses having a frequency related to the output voltage of said signal generator, said impulses produced from the impulse generator constituting said impulses of said first train of impulses from said digital generating means. 
     
     
       7. An apparatus as set forth in claim 6, in which said digital signal generating means comprises means sensitive to atmospheric temperature for producing an output voltage related to detected atmospheric temperature. 
     
     
       8. An apparatus as set forth in claim 6, in which said digital signal generating means comprises means sensitive to atmospheric pressure for producing an output voltage related to detected atmospheric pressure. 
     
     
       9. An apparatus as set forth in claim 6, in which said digital signal generating means comprises means sensitive to temperature of the engine for producing an output voltage related to the detected engine temperature. 
     
     
       10. An apparatus as set forth in claim 1, in which said predetermined position of said piston relative to the associated engine cylinder corresponds to the top-dead-center position of the piston. 
     
     
       11. An apparatus as set forth in claim 1, in which said detecting means comprises a circular disc member rotatable with the engine output shaft, a first circular ring mounted on the circumference of said disc member and having embedded therein a plurality of permanent magnets equiangularly spaced apart from each other about an axis of rotation of the disc member, the number of said permanent magnets being one half of the number of the engine cylinders associated with said output shaft, a second cylinder ring mounted on the circumference of the disc member and having a multiplicity of south and north pole sections which are disposed alternately to each other along the entire circumference of the ring, first electromagnetic pick-up means associated with said first circular ring for producing an output current when each of the permanent magnets on the disc member is magnetically linked with the pick-up means as the disc member is driven for rotation by the engine output shaft, said output current providing the impulses of said second train of pulses delivered from said detecting means, and second electromagnetic pick-up means associated with said second circular ring for producing an output current when each of the pole sections having like polarity is magnetically linked with the second electromagnetic pick-up means as the disc member is driven to rotate by the engine output shaft, said output current from said second electromagnetic pick-up means providing the impulses of said third train of pulses delivered from said detecting means.